U.S. Pat. No. 3,625,013
U.S. Pat. No. 3,779,026
U.S. Pat. No. 3,802,207
U.S. Pat. No. 3,803,854
U.S. Ser. No. 695,259, filed June 11, l976
U.S. Ser. No. 725,952, filed Sept. 23, 1976